Optical body having polyacrylate skin layer

ABSTRACT

A multilayer optical body is disclosed. The optical body includes an optical film including polyester, a first skin layer is disposed on at least one side of the polyester optical film, and a strippable skin layer is disposed on the first skin layer. The first skin layer includes a mixture of a polyacrylate and a second polymer. Methods of making such optical bodies are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Ser. No. 11/144,302, filedJun. 3, 2005 abandoned, the disclosure of which is incorporated byreference in its entirety herein.

FIELD OF THE DISCLOSURE

The present disclosure relates to optical bodies and methods of makingoptical bodies including acrylate blend layers.

BACKGROUND

Polymeric optical films are used in a wide variety of applications.Particular uses of polymeric films include mirrors and polarizers. Suchreflective films are used, for example, in conjunction with backlightsin liquid crystal displays. A polarizing film can be placed between theuser and the backlight to recycle polarized light that would beotherwise absorbed, and thereby increasing brightness. A mirror film canbe placed behind the backlight to reflect light towards the user;thereby enhancing brightness. These polymeric optical films often haveextremely high reflectivity, while being lightweight and resistant tobreakage. Thus, the films are suited for use as reflectors andpolarizers in compact electronic displays, such as liquid crystaldisplays (LCDs) placed in mobile telephones, personal data assistants,portable computers, desktop monitors, and televisions. Anotherapplication of these polarizing films includes, for example, solarcontrol.

One class of polymers useful in creating polarizer or mirror films ispolyesters, described in U.S. Pat. Nos. 5,825,543 and 5,867,316 and PCTPublications WO 99/36262 and WO 97/32226, incorporated herein byreference. One example of a polyester-based polarizer includes a stackof polyester layers of differing composition. One configuration of thisstack of layers includes a first set of birefringent layers and a secondset of layers with an isotropic index of refraction. The second set oflayers alternates with the birefringent layers to form a series ofinterfaces for reflecting light.

Although polymeric optical films can have favorable optical and physicalproperties, one limitation with some such films can be dimensionalinstability of the film when exposed to substantial fluctuations intemperature. This dimensional instability can result in formation ofwrinkles in the film as it expands and contracts. Such dimensionalinstability can be particularly common when temperatures approach orexceed approximately 80° C. Warping also may be observed when some filmsare cycled to high temperatures and high humidity conditions, such asconditions of 60° C. and 70 percent relative humidity.

Another limitation of some polymeric optical films is that they fail todissipate static charges. Static charges on a polymeric optical film canbe detrimental to the assembly of optical devices including such films,and can cause static attraction to other films or glass in the backlightdisplay. The static attraction to other films or glass in the backlightdisplay may sometimes cause visual defects manifesting themselves ascircular shadows or variations in brightness. In addition, many staticdissipative materials are not compatible with polymeric optical filmmaterials.

Another limitation of some polymeric optical films is their tendency todegrade when exposed for long periods of time to the UV light fromfluorescent bulbs in backlight displays. These optical films can becomeundesirably yellow from UV light-induced degradation.

SUMMARY

This disclosure is directed to optical bodies and methods of makingoptical bodies. More specifically, this disclosure is directed topolyester optical bodies that include polyacrylate blend skin layers andstrippable skin layers, and to co-extrusion methods of making suchoptical bodies.

One exemplary embodiment of an optical body includes an optical filmincluding polyester, an extruded inner skin layer disposed onto thepolyester optical film, and an extruded strippable skin layer disposedon top of the inner skin layer. The extruded inner skin layer includes amixture of a polyacrylate and a second polymer. In some embodiments, thesecond polymer is miscible in the polyacrylate. In other embodiments,the second polymer is not miscible or is substantially immiscible in thepolyacrylate and the second polymer has a refractive index in a rangefrom 1.45 to 1.53. In further exemplary embodiments, the second polymermay be an anti-static polymer. The skin layers can optionally includelight stabilizers and/or light absorbers.

Yet other exemplary embodiments of the disclosure include methods ofmaking an optical body. The methods include coextruding an optical layerincluding polyester with a first skin layer and a first strippable skinlayer. The first skin layer includes a mixture of a polyacrylate and asecond polymer. The first skin layer is disposed between the opticallayer and the first strippable skin layer to form an optical film. Insome embodiments, the optical film is biaxially orientated. Thestrippable skin layer can optionally be removed from the skin layer, asdesired.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing detailed description of various embodiments of the disclosurein connection with the accompanying drawings, in which:

FIG. 1 is a schematic side elevation view of one embodiment of anoptical body constructed and arranged in accordance with the disclosure;

FIG. 2 is a schematic side elevation view of another embodiment of anoptical body constructed and arranged in accordance with the disclosure;and

FIG. 3 is a plan view of an illustrative system for forming an opticalbody in accordance with of the disclosure.

DETAILED DESCRIPTION

The following description should be read with reference to the drawings,in which like elements in different drawings are numbered in likefashion. The drawings, which are not necessarily to scale, depictselected illustrative embodiments and are not intended to limit thescope of the disclosure. Although examples of construction, dimensions,and materials are illustrated for the various elements, those skilled inthe art will recognize that many of the examples provided have suitablealternatives that may be utilized.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein.

Weight percent, percent by weight, % by weight, % wt, and the like aresynonyms that refer to the concentration of a substance as the weight ofthat substance divided by the weight of the composition and multipliedby 100.

The recitation of numerical ranges by endpoints includes all numberssubsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, and 5) and any range within that range.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. For example,reference to a composition containing “a layer” encompass embodimentshaving one, two or more layers. As used in this specification and theappended claims, the term “or” is generally employed in its senseincluding “and/or” unless the content clearly dictates otherwise.

This disclosure is generally directed to optical bodies and methods ofmaking optical bodies. More specifically, this disclosure is directed topolyester optical bodies that include polyacrylate blend skin layers andstrippable skin layers, and to co-extrusion methods of making suchoptical bodies. The disclosed exemplary optical films may have improvedoptical, physical, and/or mechanical properties with the use ofpolyacrylate blend skin layers.

In many embodiments, the polyacrylate blend skin layer assists theoptical film to resist warping. In other words, warping of the opticalfilm may be reduced by use of the disclosed polyacrylate blend skinlayer with the optical film. The disclosed polyacrylate blend skin layeris considered dimensionally stable because the disclosed polyacrylateblend skin layer does not substantially warp under conditions, such aselevated temperature, elevated humidity, or both, that typically causeappreciable warpage of the optical film.

Blending or mixing miscible, immiscible or substantially immisciblepolymers into the polyacrylate skin layer provides improved resistanceto warping or buckling of the optical film when exposed to thermalcycling. In addition, the low refractive index of polyacrylates allowsthe blending with inherently anti-static polymers that have nearlymatching refractive indices without producing excessive haze. In someembodiments, these anti-static polymers are immiscible or substantiallyimmiscible in polyacrylate. In other embodiments, they may be miscible.

Polyacrylate based blends have a low ultraviolet (UV) light absorptionband edge, thus, polyacrylates are easy to protect from UV degradation.When these polyacrylate blend skin layers are loaded with UV absorbers(UVA), these polyacrylate blend skin layers protect the underlyingpolyester optical film. UVA additives include, for example, triazoles,triazines, and benzotriazoles. In some embodiments, UVA additivesinclude Tinuvin 1577 (a triazine with low volatility and highcompatibility with a variety of polymers), Tinuvin 405 (a triazineexhibiting high thermal stability and photo-permanence), and CGL-139 (ared-shifted benzotriazole exhibiting excellent photo-permanence and highsolubility into a variety of materials), all being available from CibaSpecialty Chemicals.

Polyacrylate based blend skin layers also have a number of advantageousphysical properties. Polyacrylate based blend skin layers have lowerrefractive indices that can reduce surface reflection and thus improvelight transmission through the optical film. Polyacrylate based blendskin layers have improved adhesion to film coatings and othersubstrates. Polyacrylate based blend skin layers have improved scratchresistance.

In many embodiments, a polyester optical film cannot be co-extruded witha polyacrylate skin layer without thermal degradation of thepolyacrylate skin layer. However, co-extruding an outer skin layer(e.g., a strippable skin layer) with the polyacrylate skin layer, hasbeen found to protect the polyacrylate skin layer from thermaldegradation. The outer skin layer can be subsequently removed from theskin layer to reveal a polyester optical film with a polyacrylate (orpolyacrylate blend) skin layer having advantageous properties, some ofwhich are described above.

Reference is now made to FIG. 1 and FIG. 2, which show various generalembodiments of the disclosure. In FIG. 1, optical body 10 includes anoptical film 12, a skin layer 14, and a strippable layer 16. FIG. 2illustrates another embodiment of an optical body 10. The optical bodyincludes an optical film 12 disposed between two skin layers 14. Astrippable layer 16 is disposed on each skin layer 14. The three layersin the illustrative examples depicted in FIG. 1 and FIG. 2 show thethickest layer being the optical film layer 12, followed in thickness bythe skin layer 14 and the strippable layer 16. However, the layers 12,14, 16 can be constructed to have different relative thicknesses thanthose shown in FIG. 1 and FIG. 2. These various components, along withmethods of making the optical body of the disclosure, are describedbelow.

Various optical films are suitable for use with the present disclosure.In many embodiments, the optical films are multilayer optical films,including multilayer films (whether composed of all birefringent opticallayers, some birefringent optical layers, or all isotropic opticallayers) having a high reflectivity over a wide bandwidth, andcontinuous/disperse phase optical films. These optical films includepolarizers and mirrors, for example. In general, multilayer opticalfilms can be specularly reflective and continuous/disperse phase opticalfilms can be diffusely reflective, although these characterizations arenot universal (see, e.g., the diffuse multilayer reflective polarizersdescribed in U.S. Pat. No. 5,867,316). These optical films are merelyillustrative and are not meant to be an exhaustive list of suitablepolymeric optical films useful with the present disclosure.

Both multilayer reflective polarizer optical films andcontinuous/disperse phase polarizer optical films rely on index ofrefraction differences between at least two different materials (suchas, for example, polymers) to selectively reflect light of at least onepolarization orientation. Suitable diffuse reflective polarizers includethe continuous/disperse phase reflective polarizer optical filmsdescribed in U.S. Pat. No. 5,825,543, incorporated herein by reference,as well as the diffusely reflecting polarizer optical films described inU.S. Pat. No. 5,867,316, incorporated herein by reference.

Other optical films that are suitable for use in the present disclosureare multilayer reflective polarizer films such as those described in,for example, U.S. Pat. Nos. 5,882,774 and 6,352,761 and in PCTPublication Nos. WO95/17303; WO95/17691; WO95/17692; WO95/17699;WO96/19347; and WO99/36262, all of which are incorporated herein byreference. In some embodiments, the optical film is a multilayer stackof polymer layers with a Brewster angle (the angle at which reflectanceof p-polarized light goes to zero) that is very large or nonexistent.The optical film can be made into a multilayer mirror or polarizer whosereflectivity for p-polarized light decreases slowly with angle ofincidence, is independent of angle of incidence, or increases with angleof incidence away from the normal. Commercially available forms of suchmultilayer reflective polarizers are marketed as Dual BrightnessEnhanced Film (DBEF) by 3M, St. Paul, Minn. Multilayer reflectiveoptical films are used herein as an example to illustrate optical filmstructures and methods of making and using the optical films of thedisclosure. The structures, methods, and techniques described herein canbe adapted and applied to other types of suitable optical films.

A suitable multilayer reflective optical film can be made by alternating(e.g., interleaving) uniaxially- or biaxially-oriented birefringentfirst optical layers with second optical layers. In some embodiments,the second optical layers have an isotropic index of refraction that isapproximately equal to one of the in-plane indices of the orientedlayer. The interface between the two different optical layers forms alight reflection plane. Light polarized in a plane parallel to thedirection in which the indices of refraction of the two layers areapproximately equal will be substantially transmitted. Light polarizedin a plane parallel to the direction in which the two layers havedifferent indices will be at least partially reflected. The reflectivitycan be increased by increasing the number of layers or by increasing thedifference in the indices of refraction between the first and secondlayers. Generally, multilayer optical films have 2 to 5000 opticallayers, or 25 to 2000 optical layers, or 50 to 1500 optical layers, or75 to 1000 optical layers. A film having a plurality of layers caninclude layers with different optical thicknesses to increase thereflectivity of the film over a range of wavelengths. For example, afilm can include pairs of layers which are individually tuned (fornormally incident light, for example) to achieve optimal reflection oflight having particular wavelengths. It should further be appreciatedthat, although only a single multilayer stack may be described, themultilayer optical film can be made from multiple stacks that aresubsequently combined to form the film. The described multilayer opticalfilms can be made according to U.S. Pat. No. 6,827,886 and U.S. PatentApplication Publication No. 2001/0013668, which are both incorporatedherein by reference.

A polarizer can be made by combining a uniaxially-oriented first opticallayer with a second optical layer having an isotropic index ofrefraction that is approximately equal to one of the in-plane indices ofthe oriented layer. Alternatively, both optical layers are formed frombirefringent polymers and are oriented in a multiple draw process sothat the indices of refraction in a single in-plane direction areapproximately equal. The interface between the two optical layers formsa light reflection plane for one polarization of light. Light polarizedin a plane parallel to the direction in which the indices of refractionof the two layers are approximately equal will be substantiallytransmitted. Light polarized in a plane parallel to the direction inwhich the two layers have different indices will be at least partiallyreflected. For polarizers having second optical layers with isotropicindices of refraction or low in-plane birefringence (e.g., no more thanaround 0.07), the in-plane indices (n_(x) and n_(y)) of refraction ofthe second optical layers are approximately equal to one in-plane index(e.g., n_(y)) of the first optical layers. Thus, the in-planebirefringence of the first optical layers is an indicator of thereflectivity of the multilayer optical film. Typically, it is found thatthe higher the in-plane birefringence, the better the reflectivity ofthe multilayer optical film. If the out-of-plane indices (n_(z)) ofrefraction of the first and second optical layers are equal or nearlyequal (e.g., no more than 0.1 difference, or no more than 0.05difference), the multilayer optical film also has less off-angle color.Off-angle color arises from non-uniform transmission of light at anglesother than normal to the plane of the multilayer optical film.

A mirror can be made using at least one uniaxially birefringentmaterial, in which two indices (typically along the x and y axes, orn_(x) and n_(y)) are approximately equal, and different from the thirdindex (typically along the z axis, or n_(z)). The x and y axes aredefined as the in-plane axes, in that they represent the plane of agiven layer within the multilayer film, and the respective indices n_(x)and n_(y) are referred to as the in-plane indices. One method ofcreating a uniaxially birefringent system is to biaxially orient(stretch along two axes) the multilayer polymeric film. If the adjoininglayers have different stress-induced birefringence, biaxial orientationof the multilayer film results in differences between refractive indicesof adjoining layers for planes parallel to both axes, resulting in thereflection of light of both planes of polarization. A uniaxiallybirefringent material can have either positive or negative uniaxialbirefringence. Positive uniaxial birefringence occurs when the index ofrefraction in the z direction (n_(z)) is greater than the in-planeindices (n_(x) and n_(y)). Negative uniaxial birefringence occurs whenthe index of refraction in the z direction (n_(z)) is less than thein-plane indices (n_(x) and n_(y)). If n_(1z) is selected to matchn_(2x)=n_(2y)=n_(2z) and the multilayer film is biaxially oriented,there is no Brewster's angle for p-polarized light and thus there isconstant reflectivity for all angles of incidence. Multilayer films thatare oriented in two mutually perpendicular in-plane axes are capable ofreflecting an extraordinarily high percentage of incident lightdepending of the number of layers, f-ratio, indices of refraction, etc.,and are highly efficient mirrors. Mirrors can also be made using acombination of uniaxially-oriented layers with in-plane indices ofrefraction which differ significantly.

In some embodiments, the first optical layers are birefringent polymerlayers that are uniaxially- or biaxially-oriented. Biaxial orientatationcan be accomplished either simultaneously or sequentially. Thebirefringent polymers of the first optical layers can be selected to becapable of developing a large birefringence when stretched. Depending onthe application, the birefringence may be developed between twoorthogonal directions in the plane of the film, between one or morein-plane directions and the direction perpendicular to the film plane,or a combination of these. The first polymer should maintainbirefringence after stretching, so that the desired optical propertiesare imparted to the finished film. The second optical layers can bepolymer layers that are birefringent and uniaxially- orbiaxially-oriented or the second optical layers can have an isotropicindex of refraction which is different from at least one of the indicesof refraction of the first optical layers after orientation. The secondpolymer advantageously develops little or no birefringence whenstretched, or develops birefringence of the opposite sense(positive-negative or negative-positive), such that its film-planerefractive indices differ as much as possible from those of the firstpolymer in the finished film. For many applications, it is advantageousfor neither the first polymer nor the second polymer to have anyabsorbance bands within the bandwidth of interest for the film inquestion. Thus, all incident light within the bandwidth is eitherreflected or transmitted. However, for some applications, it may beuseful for one or both of the first and second polymers to absorbspecific wavelengths, either totally or in part. The first and secondoptical layers and any optional non-optical layers of the multilayeroptical film are usually composed of polymers such as, for example,polyesters. The term “polymer” will be understood to includehomopolymers and copolymers, as well as polymers or copolymers that maybe formed in a miscible blend.

Polyesters for use in the multilayer optical films of the presentdisclosure generally include carboxylate and glycol subunits and aregenerated by reactions of carboxylate monomer molecules with glycolmonomer molecules. Each carboxylate monomer molecule has two or morecarboxylic acid or ester functional groups and each glycol monomermolecule has two or more hydroxy functional groups. The carboxylatemonomer molecules may all be the same or there may be two or moredifferent types of molecules. The same applies to the glycol monomermolecules. Also included within the term “polyester” are polycarbonatesderived from the reaction of glycol monomer molecules with esters ofcarbonic acid.

Suitable carboxylate monomer molecules for use in forming thecarboxylate subunits of the polyester layers include, for example,2,6-naphthalene dicarboxylic acid and isomers thereof; terephthalicacid; isophthalic acid; phthalic acid; azelaic acid; adipic acid;sebacic acid; norbornene dicarboxylic acid; bi-cyclooctane dicarboxylicacid; 1,6-cyclohexane dicarboxylic acid and isomers thereof; t-butylisophthalic acid, trimellitic acid, sodium sulfonated isophthalic acid;4,4′-biphenyl dicarboxylic acid and isomers thereof; and lower alkylesters of these acids, such as methyl or ethyl esters. The term “loweralkyl” refers, in this context, to C₁-C₁₀ straight or branched alkylgroups.

Suitable glycol monomer molecules for use in forming glycol subunits ofthe polyester layers include ethylene glycol; propylene glycol;1,4-butanediol and isomers thereof; 1,6-hexanediol; neopentyl glycol;polyethylene glycol; diethylene glycol; tricyclodecanediol;1,4-cyclohexanedimethanol and isomers thereof; norbornanediol;bicyclo-octanediol; trimethylol propane; pentaerythritol;1,4-benzenedimethanol and isomers thereof; bisphenol A; 1,8-dihydroxybiphenyl and isomers thereof; and 1,3-bis(2-hydroxyethoxy)benzene.

In one embodiment, the first optical layers include polyethylenenaphthalate (PEN), that can be made, for example, by reaction ofnaphthalene dicarboxylic acid with ethylene glycol. In some embodiments,polyethylene 2,6-naphthalate (PEN) is chosen as a first polymer. PEN hasa large positive stress optical coefficient, retains birefringenceeffectively after stretching, and has little or no absorbance within thevisible range. PEN also has a large index of refraction in the isotropicstate. Its refractive index for polarized incident light of 550 nmwavelength increases when the plane of polarization is parallel to thestretch direction from about 1.64 to as high as about 1.9. Increasingmolecular orientation increases the birefringence of PEN. The molecularorientation may be increased by stretching the material to greaterstretch ratios and holding other stretching conditions fixed. Anotheruseful polyester for the first optical layers is a polyethyleneterephthalate (PET) having an intrinsic viscosity of 0.74 dL/g,available from Eastman Chemical Company (Kingsport, Tenn.). Othersemicrystalline polyesters suitable as first optical layers include, forexample, polybutylene naphthalate (PBN), polyhexamethylene napthalate(PHN), polybutylene terephthalate (PBT), and polyhexamethyleneterephthalate (PHT). Suitable materials for the first optical layersinclude copolymers of PEN, PBN, PHN, PET, PBTor PHT. One example of asuitable first optical layer polymer includes coPEN having carboxylatesubunits derived from 90 mol % dimethyl naphthalene dicarboxylate and 10mol % dimethyl terephthalate and glycol subunits derived from 100 mol %ethylene glycol subunits and an intrinsic viscosity (IV) of 0.48 dL/g.The index of refraction is approximately 1.63. This polymer is hereinreferred to as low melt PEN (90/10). Additional materials useful asfirst optical layers are described, for example, in U.S. Pat. Nos.6,268,961, 6,352,761, 6,352,762, 6,498,683, 6,830,713, all incorporatedherein by reference.

Second optical layer polymers can be chosen so that in the finishedfilm, the refractive index, in at least one direction, differssignificantly from the index of refraction of the first optical layersin the same direction. Because polymeric materials are typicallydispersive, that is, the refractive indices vary with wavelength, theseconditions should be considered in terms of a particular spectralbandwidth of interest. It will be understood from the foregoingdiscussion that the choice of a second optical layer polymer isdependent not only on the intended application of the multilayer opticalfilm in question, but also on the choice made for the first opticallayer polymer, as well as processing conditions.

The second optical layers can be made from a variety of polymers havingglass transition temperatures compatible with that of the first opticallayer polymer and having a refractive index similar to the isotropicrefractive index of the first optical layer polymer. Suitable materialsfor the second optical layers include copolymers of PEN, PBN, PHN, PET,PHT, or PBT. In some embodiments, these copolymers include carboxylatesubunits which are 20 to 100 mol % second carboxylate subunits, such asnaphthalate (for coPEN or coPBN) or terephthalate (for coPET or coPBT)subunits, and 0 to 80 mol % second comonomer carboxylate subunits. Thecopolymers also include glycol subunits which are 40 to 100 mol % secondglycol subunits, such as ethylene (for coPEN or coPET) or butylene (forcoPBN or coPBT), and 0 to 60 mol % second comonomer glycol subunits. Atleast about 10 mol % of the combined carboxylate and glycol subunits aresecond comonomer carboxylate or glycol subunits.

In some embodiments, second optical layers include homopolymers ofpolymethylmethacrylate (PMMA), such as those available from IneosAcrylics, Inc., Wilmington, Del., under the trade designations CP71 andCP80, or polyethyl methacrylate (PEMA), which has a lower glasstransition temperature than PMMA. Additional second optical layerpolymers include copolymers of PMMA (coPMMA), such as a coPMMA made from75 wt % methylmethacrylate (MMA) monomers and 25 wt % ethyl acrylate(EA) monomers, (available from Ineos Acrylics, Inc., under the tradedesignation PERSPEX CP63), a coPMMA formed with MMA comonomer units andn-butyl methacrylate (nBMA) comonomer units, or a blend of PMMA andpoly(vinylidene fluoride) (PVDF) such as that available from SolvayPolymers, Inc., Houston, Tex. under the trade designation SOLEF 1008.Further second optical layer polymers include polyolefin copolymers suchas poly(ethylene-co-octene) (PE-PO) available from Dow-Dupont Elastomersunder the trade designation ENGAGE 8200, poly(propylene-co-ethylene)(PPPE) available from Fina Oil and Chemical Co., Dallas, Tex., under thetrade designation Z9470, and a copolymer of atatctic polypropylene (aPP)and isotatctic polypropylene (iPP) available from Huntsman ChemicalCorp., Salt Lake City, Utah, under the trade designation REXFLEX W111.Second optical layers can also be made from a functionalized polyolefin,such as linear low density polyethylene-g-maleic anhydride (LLDPE-g-MA)such as that available from E.I. duPont de Nemours & Co., Inc.,Wilmington, Del., under the trade designation BYNEL 4105.

In some embodiments, combinations of optical layers in the case ofpolarizers include PEN/co-PEN, PET/co-PEN, PET/co-PET, PEN/sPS,PEN/EASTAR, and PET/EASTAR, where EASTAR is polycyclohexanedimethyleneterephthalate commercially available from Eastman Chemical Co., and sPsrefers to syndiotatic polystyrene.

In some embodiments, combinations of optical layers in the case ofmirrors include PET/coPMMA, PEN/PMMA or PEN/coPMMA, PET/ECDEL,PEN/ECDEL, PEN/sPS, PEN/THV, and PEN/coPET, where ECDEL is athermoplastic polyester commercially available from Eastman ChemicalCo., and THV is a fluoropolymer commercially available from 3M Co. PMMArefers to polymethyl methacrylate and PETG refers to a copolymer of PETemploying a second glycol (usually cyclohexanedimethanol). sPS refers tosyndiotactic polystyrene.

In many embodiments, the optical films are thin. Suitable films includefilms of varying thickness, but particularly films less than 15 mils(about 380 micrometers) thick, or less than 10 mils (about 250micrometers) thick, or less than 7 mils (about 180 micrometers) thick.

In addition to the first and second optical layers, the multilayeroptical film optionally includes one or more non-optical layers such as,for example, one or more interior non-optical layers, such as, forexample, protective boundary layers between packets of optical layers.Non-optical layers can be used to give the multilayer film structure orto protect it from harm or damage during or after processing. Thenon-optical layers may be of any appropriate material and can be thesame as one of the materials used in the optical stack. Of course, it isimportant that the material chosen not have optical propertiesdeleterious to those of the optical stack. In many embodiments, thepolymers of the first optical layers, the second optical layers, and thenon-optical layers are chosen to have similar rheological properties(e.g., melt viscosities) so that they can be co-extruded without flowdisturbances. In some embodiments, the second optical layers, and othernon-optical layers have a glass transition temperature, T_(g), that canbe either below or no greater than about 40° C. above the glasstransition temperature of the first optical layers. In some embodiments,the glass transition temperature of the second optical layers, andnon-optical layers is below the glass transition temperature of thefirst optical layers.

The thickness of the non-optical layers can be at least four times, orat least 10 times, and can be at least 100 times, the thickness of atleast one of the individual first and second optical layers. Thethickness of the non-optical layers can be selected to make a multilayeroptical film having a particular thickness.

While the multilayer optical stacks, as described above, can providesignificant and desirable optical properties, other properties, whichmay be mechanical, optical, or chemical, are difficult to provide in theoptical stack itself without degrading the performance of the opticalstack. Such properties may be provided by including one or more layerswith the optical stack that provide these properties while notcontributing to the primary optical function of the optical stackitself. Since these layers are typically provided on the major surfacesof the optical stack, they are often known as “skin layers.”

In typical exemplary embodiments of the present disclosure, skin layersinclude a mixture of acrylate polymers (polyacrylates) and anotherpolymer to form a polyacrylate blend skin layer. As described above, thepolyacrylate blend skin layer can provide a number of useful properties.In many embodiments, the polyacrylate blend skin layer is normallytransparent or transmissive or substantially transparent or transmissivefor light within a desired wavelength range.

The polyacrylate blend skin layer(s) can be selected such that it can beextruded, remains transparent after processing at high temperatures, andis substantially stable at temperatures from at least about −30° C. to85° C. In many embodiments, the polyacrylate blend skin layer isnormally flexible, but does not significantly expand in length or widthover the temperature range of −30° C. to 85° C. To the extent that thepolyacrylate blend skin layer does expand over this temperature range,the expansion is substantially uniform such that the film does not showexcessive wrinkling. In some embodiments, the polyacrylate blend skinlayer includes, as a primary component, a polyacrylate materialexhibiting a glass transition temperature (T_(g)) from 55 to 200° C., orfrom 85 to 160° C.

The thickness of the polyacrylate blend skin layer can vary dependingupon the application. In many embodiments, the polyacrylate blend skinlayer is from 0.1 to 10 mils (about 2 to 250 micrometers) thick, or from0.5 to 8 mils (about 12 to 200 micrometers) thick, or from 1 to 7 mils(about 25 to 180 micrometers) thick.

The polyacrylate blend skin layer can include a mixture of homopolymersand/or copolymers of polyacrylate and a second polymer that is differentfrom the polyacrylate. In some embodiments, the second polymer ismiscible in the polyacrylate. In other embodiments, the second polymeris immiscible or substantially immiscible in the polyacrylate. In theseimmiscible embodiments, the second polymer can have a refractive indexvalue within 0.05 or 0.04 or 0.03, or 0.02 or 0.01 of the polyacrylaterefractive index value. In some immiscible embodiments, the secondpolymer has a refractive index in a range from 1.45 to 1.53 or from 1.46to 1.51. The second polymer can be any useful polymer such as, forexample, anti-static polymers, functionalized copolymers for improvedadhesion to other polymer layers, and elastomeric polymers for improvedimpact resistance.

The second polymer can be used at any useful level in the polyacrylateblend skin layer. In some embodiments, the second polymer can be presentin the polyacrylate blend skin layer in a range from 1 to 40 weight, or1 to 30 weight percent, or at 5 to 20 weight percent of the material ofthe polyacrylate blend skin layer.

Useful anti-static materials include, for example, polyether copolymers(such as, for example, polyethylene glycol), Irgastat™ P18 from CibaSpecialty Chemicals, LR-92967 from Ampacet, Tarrytown, N.Y., Pelestat™NC6321 and Pelestat™ NC7530 from Tomen America Inc., New York, N.Y., andionic polymers, such as, for example, the static dissipative polymerblends (e.g., Stat-Rite™ polymer products) manufactured by Noveon, Inc.,Cleveland, Ohio, further anti-static polymers include Pelestat™ 300(Available from Sanyo Chemicals), Pelestat™ 303, Pelestat™ 230,Pelestat™ 6500, Statrite M809 (Available from Noveon), Stat-Rite™ x5201,Stat-Rite™ x5202, Irgastat™ P16 (available from Ciba Chemicals).

In some exemplary embodiments, anti-static materials can be used atlevels of approximately 1 to 30 weight percent of the material of thepolyacrylate blend skin layer, or at 5 to 20 weight percent.

In some embodiments, polyacrylate blend skin layer includes homopolymersof polymethylmethacrylate (PMMA), such as those available from IneosAcrylics, Inc., Wilmington, Del., under the trade designations CP71 andCP80, or those available from Atohass North America, Inc., under thetrade designations VO44, or polyethyl methacrylate (PEMA), which has alower glass transition temperature than PMMA. In other embodiments,polyacrylate blend skin layer can include copolymers of PMMA (coPMMA),such as a coPMMA made from 75 wt % methylmethacrylate (MMA) monomers and25 wt % ethyl acrylate (EA) monomers, (available from Ineos Acrylics,Inc., under the trade designation PERSPEX CP63), or a coPMMA formed withMMA comonomer units and n-butyl methacrylate (nBMA) comonomer units. Inone embodiment, the polyacrylate blend skin layer includes a mixture orblend of PMMA and poly(vinylidene fluoride) (PVDF) such as thatavailable from Solvay Polymers, Inc., Houston, Tex. under the tradedesignation SOLEF 1008. In addition, functionalized copolymers of PMMAsuch as ELVACITE 2044, ELVACITE 2045, ELVACITE 2895, ELVACITE 4026, andELVACITE 4400 (all available from Lucite) can be blended with PMMA orother copolymers of PMMA to improve physical properties such asflexibility, impact resistance and adhesion to other polymer layers.

In one particular embodiment, the optical film includes PEN or coPEN andthe polyacrylate blend skin layer includes PMMA. In another particularembodiment, the optical film includes PET or coPET and the polyacrylateblend skin layer includes coPMMA. Strippable skin layers including apolyolefin such as, for example, polypropylene, can be disposed on thepolyacrylate blend skin layer of either embodiment.

In some embodiments, the polyacrylate blend skin layer includes a UVlight absorber (UVA) and/or a hindered amine light stabilizer (HALS). UVlight absorber can function by competitively absorbing UV energy thatcan cause photodegradation of a structure. A wide variety of ultravioletlight absorbing compounds are commercially available including, forexample, benzophenones (available under the CYASORB tradename, CytecIndus., Wester Peterson, N.J.) and triazines (available under theTINUVIN tradename, Ciba Specialty Chemicals). In some embodiments, a UVlight absorber is present in the polyacrylate blend skin layer in anamount between 0.25% and 10% by weight of polyacrylate blend skin layeror from 1% to 5% by weight of polyacrylate blend skin layer.

Alternatively or in addition to the UVA, the polyacrylate blend skinlayer can include a hindered amine light stabilizer (HALS). A widevariety of HALS are commercially available including, for example, underthe tradenames TINUVIN or CHIMASSORB from Ciba Specialty Chemicals orunder the tradename LOWILITE from Great Lake Chemical Corp. In someembodiments, a HALS is present in the polyacrylate blend skin layer inan amount between 0.25% and 10% by weight of polyacrylate blend skinlayer or from 1% to 5% by weight of polyacrylate blend skin layer.

The polyacrylate blend skin layer can be formed such that it diffuseslight. The diffusion property can be accomplished by using an inherentlydiffuse polymeric material, by imparting a diffuse pattern onto thepolyacrylate blend skin layer during manufacture or further processing,e.g., by applying a rough strippable skin layer (described below) to thepolyacrylate blend skin layer during co-extrusion. Light diffusivefeatures in the polyacrylate blend skin layer can also be accomplishedby incorporation of small particles with refractive indices differingfrom that of the polyacrylate blend skin layer, or with additives thatinduce voiding in the polyacrylate skin layer.

The roughened surface formed by the rough strippable skin layer or byaddition of particles to the polyacrylate blend skin layer can lower thefilm's coefficient of friction thus reducing the film's tendency toadhere to adjacent surfaces such as glass or other rigid films. Reducingthe film's adherence to adjacent surfaces removes or reduces the impactof an additional constraint (e.g., an adjacent glass or film surface) onthe film that would otherwise contribute to film warpage.

For many applications, it may be desirable to include sacrificialprotective skins disposed on the polyacrylate blend skin layer, wherethe interfacial adhesion between the skin layer(s) and the polyacrylateblend skin layer is controlled so that the skin layers can be strippedfrom the polyacrylate blend skin layer before use. In some embodiments,it is beneficial if these sacrificial skins have sufficient adhesion tothe polyacrylate blend skin layers that they can be re-applied afterinspection of the film. These strippable skin layers can be used toprotect the underlying optical body during storage and shipping. Thestrippable skin layers can be removed prior to use of the optical film.The strippable skin layers can be disposed onto the polyacrylate blendskin layer by coating, extrusion, or other suitable methods. In manyembodiments, the strippable skin layer is formed by coextrusion with thepolyacrylate blend skin layer. The strippable skin layers can be formedusing any protective polymer material that has sufficient adherence(with or without adhesive as desired) to the polyacrylate blend skinlayer so that the strippable skin layer will remain in place until thestrippable skin layer is removed manually or mechanically. Suitablematerials include, for example, polyolefins and, in some embodiments,low melting and low crystallinity polyolefins such as copolymers ofsyndiotactic polypropylene (for example, FINAPLAS 1571 from TotalPetrochemical), copolymers of propylene and ethylene (for example,PP8650 from Total Petrochemical), or ethylene octene copolymers (forexample, AFFINITY PT 1451 from Dow). Optionally, a mixture of polyolefinmaterials can be utilized for the strippable skin layer. In someembodiments, the strippable skin material has a melting point of 80° C.to 145° C. according to differential scanning calorimetry (DSC)measurement, or a melting point of 90° C. to 135° C., as desired. Theskin layer resin can have a melt flow index of 7 to 18 g/10 minutes, or10 to 14 g/10 minutes as measured according to ASTM D1238-95 (“FlowRates of Thermoplastics by Extrusion Plastometer”), incorporated hereinby reference, at a temperature of 230° C. and a force of 21.6N.

In many embodiments, when the strippable skin layer is removed therewill be no remaining material from the strippable skin layer or anyassociated adhesive, if used. In some embodiments, the strippable skinlayer has a thickness of at least 12 micrometers. Optionally, thestrippable skin layer includes a dye, pigment, or other coloringmaterial so that it is easy to observe whether the strippable skin layeris on the optical body or not. This can facilitate proper use of theoptical body. Other materials can be blended into the strippable skinlayer to improve adhesion to the polyacrylate blend skin layers.Modified polyolefins containing vinyl acetate or maleic anhydride may beparticularly useful for improving adhesion of the strippable skin layersto the polyacrylate blend skin layers.

In some exemplary embodiments, the materials of one or more strippableskin layers may be selected so that the adhesion of the skin(s) to thepolyacrylate blend skin layer is characterized by a peel force of atleast 2 g/in or more, or characterized by a peel force of a 4, 5, 10 or15 g/in or more. In some exemplary embodiments, the optical bodies canbe characterized by a peel force as high as 100 g/in or even 120 g/in.In other exemplary embodiments, the optical bodies can be characterizedby a peel force of 50, 35, 30 or 25 g/in or less. In some exemplaryimplementations the adhesion can be in the range from 2 g/in to 120g/in, from 4 g/in to 50 g/in, from 5 g/in to 35 g/in, or from 15 g/in to25 g/in. In other exemplary embodiments, the adhesion can be withinother suitable ranges. Peel forces over 120 g/in can be tolerated forsome applications.

The peel force that can be used to characterize exemplary embodiments ofthe present disclosure can be measured as follows. In particular, thepresent test method provides a procedure for measuring the peel forceneeded to remove a strippable skin layer from an optical film (e.g.,multilayer film, polycarbonate, etc.). Test-strips are cut from theoptical body with a strippable skin layer adhered to the optical film.The strips are typically about 1″ width, and more than about 6″ inlength. The strips may be pre-conditioned for environmental agingcharacteristics (e.g., hot, hot & humid, cold, thermal-shock).Typically, the samples should dwell for more than about 24 hours priorto testing. The 1″ strips are then applied to rigid plates, for example,using double-sided tape (such as Scotch™ double sided tape availablefrom 3M), and the plate/test-strip assembly is fixed in place on thepeel-tester platen. The leading edge of the strippable skin is thenseparated from the optical film and clamped to a fixture connected tothe peel-tester load-cell. The platen holding the plate/test-stripassembly is then carried away from the load-cell at constant speed ofabout 90 inches/minute, effectively peeling the strippable skin layerfrom the substrate optical film at about an 180 degree angle. As theplaten moves away from the clamp, the force required to peel thestrippable skin layer off the film is sensed by the load cell andrecorded by a microprocessor. The force required for peel is thenaveraged over 5 seconds of steady-state travel (preferably ignoring theinitial shock of starting the peel) and recorded.

Other materials suitable for use in the strippable skin layer(s)include, for example, fluoropolymers such as polyvinylidene fluoride(PVDF), ethylene-tetrafluoroethylene fluoropolymers (ETFE),polytetrafluoroethylene (PTFE), copolymers of PMMA (or a coPMMA) andPVDF, or any of the THV or PFA materials available from 3M (St. Paul,Minn.). Processing aids such as DYNAMAR (available from 3M) or GLYCOLUBE(available fro Lonza Corporation in Fair Lawn, N.J.) may enhance releasecharacteristics of strippable skin layers.

Materials suitable for use in the strippable skin layer(s) generallyinclude polyolefins, such as polypropylene and modified polypropylenes.Aliphatic polyolefins can be used. One suitable group of polypropylenesincludes high density polypropylenes which exhibit particularly lowadhesion to polyester and acrylic materials, and which are commonly usedto make multilayer optical films. Polyethylene and their copolymers arealso may be useful, including copolymers and propylene and ethylene.Other exemplary materials include polymethylpentene, cyclic olefincopolymers such as TOPAS available from Ticona Engineering Polymers(Florence, Ky.), copolymers of olefins with maleic anhydride, acrylicacid, or glycidyl methacrylate, or any of the HYTREL (thermoplasticpolyester elastomer) or BYNEL (modified ethylene vinyl acetate)materials available from DuPont Corporation (Wilmington, Del.).

Syndiotactic and atactic vinyl aromatic polymers, which may be useful insome embodiments of the present disclosure, include poly(styrene),poly(alkyl styrene), poly(styrene halide), poly(alkyl styrene),poly(vinyl ester benzoate), and these hydrogenated polymers andmixtures, or copolymers containing these structural units. Examples ofpoly(alkyl styrenes) include: poly(methyl styrene), poly(ethyl styrene),poly(propyl styrene), poly(butyl styrene), poly(phenyl styrene),poly(vinyl naphthalene), poly(vinylstyrene), and poly(acenaphthalene)may be mentioned. As for the poly(styrene halides), examples include:poly(chlorostyrene), poly(bromostyrene), and poly(fluorostyrene).Examples of poly(alkoxy styrene) include: poly(methoxy styrene), andpoly(ethoxy styrene). Among these examples, as particularly preferablestyrene group polymers, are: polystyrene, polyp-methyl styrene),poly(m-methyl styrene), polyp-tertiary butyl styrene),poly(p-chlorostyrene), poly(m-chloro styrene), polyp-fluoro styrene),and copolymers of styrene and p-methyl styrene may be mentioned.Furthermore, as comonomers of syndiotactic vinyl-aromatic groupcopolymers, besides monomers of above explained styrene group polymer,olefin monomers such as ethylene, propylene, butene, hexene, or octene;diene monomers such as butadiene, isoprene; polar vinyl monomers such ascyclic diene monomer, methyl methacrylate, maleic acid anhydride, oracrylonitrile may be mentioned.

Aliphatic copolyesters and aliphatic polyamides may also be usefulmaterials for strippable boundary layers. As for polyester polymers andcopolymers, the diacids can be chosen from terephthalic acid,isophthalic acid, phthalic acid, all isomeric naphthalenedicarboxylicacids (2,6-, 1,2-, 1,3-, 1,4-, 1,5-, 1,6-, 1,7-, 1,8-, 2,3-, 2,4-, 2,5-,2,7-, and 2,8-), bibenzoic acids such as 4,4′-biphenyl dicarboxylic acidand its isomers, trans-4,4′-stilbene dicarboxylic acid and its isomers,4,4′-diphenyl ether dicarboxylic acid and its isomers,4,4′-diphenylsulfone dicarboxylic acid and its isomers,4,4′-benzophenone dicarboxylic acid and its isomers, halogenatedaromatic dicarboxylic acids such as 2-chloroterephthalic acid and2,5-dichloroterephthalic acid, other substituted aromatic dicarboxylicacids such as tertiary butyl isophthalic acid and sodium sulfonatedisophthalic acid, cycloalkane dicarboxylic acids such as1,4-cyclohexanedicarboxylic acid and its isomers and2,6decahydronaphthalene dicarboxylic acid and its isomers, bi- ormulti-cyclic dicarboxylic acids (such as the various isomeric norbornaneand norbornene dicarboxylic acids, adamantane dicarboxylic acids, andbicyclo-octane dicarboxylic acids), alkane dicarboxylic acids (such assebacic acid, adipic acid, oxalic acid, malonic acid, succinic acid,glutaric acid, azelaic acid, and dodecane dicarboxylic acid), and any ofthe isomeric dicarboxylic acids of the fused-ring aromatic hydrocarbons(such as indene, anthracene, pheneanthrene, benzonaphthene, fluorene andthe like). Alternatively, alkyl esters of these monomers, such asdimethyl terephthalate, may be used.

Suitable diol comonomers include but are not limited to linear orbranched alkane diols or glycols (such as ethylene glycol, propanediolssuch as trimethylene glycol, butanediols such as tetramethylene glycol,pentanediols such as neopentyl glycol, hexanediols,2,2,4-trimethyl-1,3-pentanediol and higher diols), ether glycols (suchas diethylene glycol, triethylene glycol, and polyethylene glycol),chain-ester diols such as3-hydroxy-2,2-dimethylpropyl-3-hydroxy-2,2-dimethyl propanoate,cycloalkane glycols such as 1,4-cyclohexanedimethanol and its isomersand 1,4-cyclohexanediol and its isomers, bior multicyclic diols (such asthe various isomeric tricyclodecane dimethanols, norbornane dimethanols,norbornene dimethanols, and bicyclo-octane dimethanols), aromaticglycols (such as 1,4-benzenedimethanol and its isomers, 1,4-benzenedioland its isomers, bisphenols such as bisphenol A, 2,2′-dihydroxy biphenyland its isomers, 4,4′dihydroxymethyl biphenyl and its isomers, and1,3-bis(2-hydroxyethoxy)benzene and its isomers), and lower alkyl ethersor diethers of these diols, such as dimethyl or diethyl diols.

In some embodiments, one or more strippable skin layers are roughstrippable skin layer or layers. The rough strippable skin layer canassist in forming a rough polyacrylate blend skin layer surface asdescribed above. It has been found that these and related goals can beaccomplished by careful selection of the materials for making thecontinuous phase and the disperse phase and ensuring their compatibilitywith at least some of the materials used to make the optical layerand/or polyacrylate blend skin layer. In some embodiments, thecontinuous phase of the rough strippable skin layers have lowcrystallinity or are sufficiently amorphous in order to remain adheredto the polyacrylate blend skin layer for a desired period of time.

In many embodiments, the degree of adhesion of the rough strippable skinlayers to an adjacent surface or surfaces of the polyacrylate blend skinlayer(s), as well as the degree of surface roughness, can be adjusted tofall within a desired range by blending in more crystalline or lesscrystalline materials, more adhesive or less adhesive materials, or bypromoting the formation of crystals in one or more of the materialsthrough subsequent processing steps. In some exemplary embodiments, twoor more different materials with different adhesions can be used asco-continuous phases included into the continuous phase of the roughstrippable skin layers. For example, a material with relatively highcrystallinity, such as high density polyethylene (HDPE) orpolycaprolactone, can be blended into the rough strippable skin layersin order to impart rough texture into the surface of a polyacrylateblend skin layer that is adjacent to the rough strippable skin layer andto affect adhesion. Nucleating agents can also be blended into the roughstrippable skin layers in order to adjust the rate of crystallization ofone or more of the phases in the strippable skin composition. In someexemplary embodiments, pigments, dyes or other coloring agents can beadded to the materials of the rough strippable skins for improvedvisibility of the skin layers.

The degree of surface roughness of the rough strippable skin layers canbe adjusted similarly by mixing or blending different materials, forexample, polymeric materials, inorganic materials, or both into thedisperse phase. In addition, the ratio of disperse phase to continuousphase can be adjusted to control the degree of surface roughness andadhesion and will depend on the particular materials used. Thus, one,two or more polymers would function as the continuous phase, while one,two or more materials, which may or may not be polymeric, would providea disperse phase with a suitable surface roughness for imparting asurface texture. The one or more polymers of the continuous phase can beselected to provide a desired adhesion to the material of thepolyacrylate blend skin layer. For example, HDPE could be blended intolow crystallinity syndiotactic polypropylene (sPP) for improving surfaceroughness along with a low crystallinity poly(ethylene octene) (PE-PO)for improving strippable skin adhesion.

Where the disperse phase is capable of crystallization, the roughness ofthe strippable skin layer or layers can be enhanced by crystallizationof this phase at an appropriate extrusion processing temperature, degreeof mixing, and quenching, as well as through addition of nucleationagents, such as aromatic carboxylic-acid salts (sodium benzoate);dibenzylidene sorbitol (DBS), such as MILLAD 3988 from Milliken &Company; and sorbitol acetals, such as IRGACLEAR clarifiers by CibaSpecialty Chemicals and NC-4 clarifier by Mitsui Toatsu Chemicals. Othernucleators include organophosphate salts and other inorganic materials,such as ADKSTAB NA-11 and NA-21 phosphate esters from Asahi-Denka andHYPERFORM HPN-68, a norbornene carboxylic-acid salt from Milliken &Company. In some exemplary embodiments, the disperse phase includesparticles, such as those including organic and/or inorganic materials,that will protrude from the surface of the rough strippable skin layersand impart surface structures into the polyacrylate blend skin layerwhen the optical body is processed, e.g., extruded, oriented orlaminated together.

The disperse phase of the rough strippable skin layers can includeparticles or other rough features that are sufficiently large (forexample, at least 0.1 micrometers average diameter) to be used to imparta surface texture into the outer surface of an adjacent layer of thepolyacrylate blend skin layer by application of pressure and/ortemperature to the polyacrylate blend skin layer with the roughstrippable skin layer or layers. At least a substantial portion ofprotrusions of the disperse phase should typically be larger than thewavelength of the light it is illuminated with but still small enoughnot to be resolved with an unaided eye. Such particles can includeparticles of inorganic materials, such as silica particles, talcparticles, sodium benzoate, calcium carbonate, a combination thereof orany other suitable particles. Alternatively, the disperse phase can beformed from polymeric materials that are (or become) substantiallyimmiscible in the continuous phase under the appropriate conditions.

The disperse phase can be formed from one or more materials, such asinorganic materials, polymers, or both that are different from at leastone polymer of the continuous phase and immiscible therein, with thedisperse polymer phases having typically a higher degree ofcrystallinity than the polymer or polymers of the continuous phase. Insome exemplary embodiments, the use of more than one material for thedisperse phase can result in rough features or protrusions of differentsizes or compounded protrusions, such as “protrusion-on-protrusion”configurations. Such constructions can be beneficial for creating haziersurfaces on optical films. In some embodiments, the disperse phase isonly mechanically miscible or immiscible with the continuous phasepolymer or polymers. The disperse phase material or materials and thecontinuous phase material or materials can phase separate underappropriate processing conditions and form distinct phase inclusionswithin the continuous matrix, and particularly at the interface betweenthe optical film and the rough strippable skin layer.

Exemplary polymers that are particularly suitable for use in thedisperse phase include styrene acrylonitrile, modified polyethylene,polycarbonate and copolyester blend, ε-caprolactone polymer, such asTONE™ P-787, available from Dow Chemical Company, random copolymer ofpropylene and ethylene, other polypropylene copolymers, poly(ethyleneoctene) copolymer, anti-static polymer, high density polyethylene,medium density polyethylene, linear low density polyethylene andpolymethyl methacrylate. The disperse phase of the rough strippable skinlayers may include any other appropriate material, such as any suitablecrystallizing polymer and it may include the same materials as one ormore of the materials used in the optical film.

Materials suitable for use in the continuous phase of the strippablelayer include, for example, polyolefins, such as low melting and lowcrystallinity polypropylenes and their copolymers; low melting and lowcrystallinity polyethylenes and their copolymers, low melting and lowcrystallinity polyesters and their copolymers, or any suitablecombination thereof. Such low melting and low crystallinitypolypropylenes and their copolymers consist of propylene homopolymersand copolymers of propylene and ethylene or alpha-olefin materialshaving between 4 to 10 carbon atoms. The term “copolymer” includes notonly the copolymer, but also terpolymers and polymers of four or morecomponent polymers. Suitable low melting and low crystallinitypolypropylenes and their copolymers include, for example, syndiotacticpolypropylene (such as, FINAPLAS 1571 from Total Petrochemicals, Inc.),which is a random copolymer with an extremely low ethylene content inthe syndiotactic polypropylene backbone, and random copolymers ofpropylene (such as PP8650 or PP6671 from Total Petrochemical, which isnow Total Petrochemicals, Inc.) The described copolymers of propyleneand ethylene can also be extrusion blended with homopolymers ofpolypropylene to provide a higher melting point skin layer if needed.

Other suitable low melting and low crystallinity polyethylenes andpolyethylene copolymers include, for example, linear low densitypolyethylene and ethylene vinyl alcohol copolymers. Suitablepolypropylenes include, for example, random copolymers of propylene andethylene (for example, PP8650 from Total Petrochemicals, Inc.), orethylene octene copolymers (for example, AFFINITY PT 1451 from DowChemical Company). In some embodiments, the continuous phase includes anamorphous polyolefin, such as an amorphous polypropylene, amorphouspolyethylene, an amorphous polyester, or any suitable combinationthereof or with other materials. In some embodiments, the materials ofthe rough strippable skin layers can include nucleating agents, such assodium benzoate to control the rate of crystallization. Additionally,anti-static materials, anti-block materials, coloring agents such aspigments and dyes, stabilizers, and other processing aids may be addedto the continuous phase. Additionally or alternatively, the continuousphase of the rough strippable skin layers may include any otherappropriate material. In some exemplary embodiments, migratoryantistatic agents can be used in the rough strippable skin layers tolower their adhesion to the optical films.

The polyacrylate blend skin layer can be added to opposing sides of theoptical film. However, in some implementations the polyacrylate blendskin layer is added to just one side of the optical film. In some suchexemplary embodiments, the presence of one polyacrylate blend skin layermay encourage curling of the film, such as for making an optical bodythat will wrap around a fluorescent light tube.

The optical body can also optionally include one or more layers inaddition to the optical film, the polyacrylate blend skin layer, and thestrippable layer. When one or more additional layers are present, theycan function to improve the integrity of the composite optical body. Inparticular, the layers can serve to bind the optical film to thepolyacrylate blend skin layer.

Various additional compounds can be added, including the comonomerspreviously listed in the optical film. Extrusion aids such asplasticizers and lubricants can be added for improved processing andadhesion to other layers. Also, particles such as inorganic spheres orpolymer beads with a different refractive index from the adhesivepolymer can be used.

During processing, the polyacrylate blend skin layer and peelable(strippable) skin layer(s) can be extrusion coated together with theoptical film at temperatures exceeding 250° C. Therefore, the opticalfilm polymers should be able to withstand exposure to temperaturesgreater than 250° C. In many embodiments, the optical film undergoesvarious rolling steps during processing, and is flexible. The strippablelayer or layers can be thermally stable in a melt phase at temperaturesabove 220° C. Thus, the strippable layer should not substantiallydegrade during extrusion at temperatures greater than 220° C. Thestrippable layer can be less than 2 mils (about 50 micrometers) thick,or less than 1 mil (about 25 micrometers) thick, or less than 0.5 mil(about 12 micrometers) thick.

Various methods may be used for forming the composite optical body ofthe present disclosure. As stated above, the optical bodies can take onvarious configurations, and thus the methods vary depending upon theparticular configuration of the final optical body. A step common to allmethods of forming the composite optical body is adhering the opticalfilm to the polyacrylate blend skin layer. This step can be conductedconcurrently with or subsequently to making the optical film and in avariety of ways, such as co-extruding various layers, extrusion coatingthe layers, or co-extrusion coating of the layers (such as when apolyacrylate blend skin layer and an intermediate layer aresimultaneously extrusion coated onto the optical film).

FIG. 4 shows a schematic plan view of an illustrative system for formingan optical body in accordance with the disclosure. The system 20includes a plurality of feed blocks 22, 24 and 26 providing material toan extruder 30 for co-extrusion. While five feed blocks are shown, anyuseful number of feed blocks may be included in the co-extrusion system20. The illustrated feed blocks include an optical film feed block 22,two polyacrylate blend skin layer feed blocks 24, and two strippableskin feed blocks 26.

The extruder co-extrudes the materials from the feed blocks into asingle multilayer optical film 36. In the illustrated embodiment, themultilayer optical film 36 travels between and over several rolls 32, 34and placed onto a winder 38. After cooling, the multi-layer optical film36 can be subsequently processed, such as by cutting into sheets.

In some embodiments, the co-extruded film can be oriented by stretchingindividual sheets of the optical body material in heated air. Foreconomical production, stretching may be accomplished on a continuousbasis in a standard length orienter, tenter oven, or both, or using anyother suitable stretcher. Economies of scale and line speeds of standardpolymer film production may be achieved thereby achieving manufacturingcosts that are substantially lower than costs associated withcommercially available absorptive polarizers.

One method of creating a birefringent system is to biaxially stretch ordraw (e.g., stretch along two dimensions) a multilayer stack in which atleast one of the materials in the stack has its index of refractionaffected by the stretching process (e.g., the index either increases ordecreases). Biaxial stretching of the multilayer stack may result indifferences between refractive indices of adjoining layers for planesparallel to both axes thus resulting in reflection of light in bothplanes of polarization. Specific methods and materials are taught in PCTpatent application WO 99/36812, incorporated herein by reference in itsentirety.

For example, to make a mirror, two uniaxially stretched polarizingsheets are positioned with their respective orientation axes rotated 90°C., or the sheet is biaxially stretched. Biaxially stretching themultilayered sheet will result in differences between refractive indicesof adjoining layers for planes parallel to both axes thereby resultingin reflection of light in both planes of polarization directions.

In other exemplary embodiments, the optical bodies constructed accordingto the present disclosure may be stretched or drawn uniaxially orsubstantially uniaxially (e.g., along the machine direction or along thedirection substantially orthogonal to the machine direction). Where anoptical film included into an optical body of the present disclosure isa reflective polarizer, it may be beneficial for the optical body to bedrawn uniaxially or substantially uniaxially in the transverse direction(TD), while allowed to relax in the machine direction (MD) as well asthe normal direction (ND). Suitable methods and apparatuses that can beused to draw such exemplary embodiments of the present disclosure aredescribed in U.S. Application Publication Nos. 2002/0190406,2002/0180107, 2004/0099992 and 2004/0099993, the disclosures of whichare hereby incorporated by reference herein.

The pre-stretch temperature, stretch temperature, stretch rate, stretchratio, heat set temperature, heat set time, heat set relaxation, andcross-stretch relaxation are selected to yield a multilayer devicehaving the desired refractive index relationship. These variables areinter-dependent; thus, for example, a relatively low stretch rate couldbe used if coupled with, e.g., a relatively low stretch temperature. Itwill be apparent to one of ordinary skill how to select the appropriatecombination of these variables to achieve the finished article withdesired properties. In many embodiments, a stretch ratio is in the rangefrom 1:2 to 1:10, or from 1:3 to 1:7 in the machine or transversedirection and from 1:0.5 to 1:10, or from 1:0.5 to 1:7 orthogonal to themachine or transverse direction.

EXAMPLES Methods

One example of a method for observing warp is as follows: Clean two9.5″×12.5″ (24.1×31.8 cm) flat pieces of double strength glass withisopropyl alcohol. A 9″×12″ (22.9×30.5 cm) piece of the optical body isattached to one piece of glass on two short sides and one of the longsides, leaving the remaining long side unconstrained. To attach theoptical body, first attach Double Stick Tape (3M, St. Paul, Minn.) to apiece of glass such that the tape is 0.5″ (1.3 cm) from three edges ofthe glass and will be exactly covered by 3 sides of the optical body.Avoid overlapping the ends of the tape. Place the optical body on thetape such that the optical body is tensioned across the tape and is heldabove the glass surface by the thickness of the tape (about 0.1 mm).Roll the optical body down to the tape with a 4.5 lb. (2 kg) roller oncein each direction, avoiding extra force.

Place three 0.1 mm thick, 0.5″ (1.3 cm) wide polyethylene terephthalate(PET) shims onto the rolled optical body, the shims being exactly abovethe tape and of the same lengths, but on the opposite sides of theoptical body. Avoid overlapping the shims. Place the top piece of glasson top of the shims and exactly aligned with the bottom piece of glass.

This completes a sandwiched construction of glass-tape-opticalfilm-shim-glass, in which the optical body is constrained at three edgesand substantially free floating in the center. This construction isattached together with 4 binder clips as are commonly used to holdstacks of paper together (Binder Clips, Officemate InternationalCorporation, Edison, N.J.). The clips should be of an appropriate sizeto apply pressure to the center of the tape (approximately 0.75″ (1.9cm) from the edge of the glass) and are positioned two each on the shortsides of the construction, each about 0.75″ (1.9 cm) away from thebottom and top of the optical body.

This completed construction is placed in a thermal shock chamber (ModelSV4-2-2-15 Environmental Test Chamber, Envirotronics, Inc., GrandRapids, Mich.) and subjected to 96 cycles, a cycle consisting of onehour at 85° C. followed by one hour at −35° C. The film is then removedfrom the chamber and inspected for wrinkles. Warpage is consideredunacceptable when there are many deep wrinkles across the surface of thefilm. When there are few shallow wrinkles or the film appears smooth,warpage is generally considered acceptable.

Example 1

A multi-layer reflective polarizer was constructed with first opticallayers comprising PEN (polyethylene naphthalate) and second opticallayers comprising coPEN (copolyethelene naphthalate). The PEN and coPENwere coextruded through a multi-layer melt manifold and multiplier toform 825 alternating first and second optical layers. This multi-layerfilm also contained two internal and two external protective boundarylayers of the same coPEN as the second optical layers for a total of 829layers. In addition, two external skin layers were coextruded on bothsides the optical layer stack. These polyacrylate blend skin layer wereabout 18 micrometers thick and comprised 95 wt. % PMMA (VO44 from TotalPetrochemical) and 5 wt. % anti-static polymer (PELESTAT 6321 from SanyoChemical Industries). Strippable skin layers formed from a blend of 96wt % syndiotactic polypropylene (PP1571 from Total Petrochemical) and 4wt. % anti-static polymer (PELESTAT 300 from Sanyo Chemical Industries)were formed over the PMMA blend structural layers. An extruded cast webof the above-construction was then heated in a tentering oven with airat 150° C. for 45 seconds and then uniaxially oriented at a 6:1 drawratio.

Samples were prepared, as described above, where one sample did not havea polyacrylate skin layer, one sample had a polyacrylate skin layer, andtwo samples had a polyacrylate/PELESTAT 6321 blend skin layer at 5 wt. %and 10 wt. % PELESTAT 6321. Warp testing indicated that the optical bodywith the PMMA/PELESTAT blend polyacrylate blend skin layer samples hadbetter warp resistance than a similar optical body with no polyacrylateskin layers and better warp resistance than a similar optical body withthe polyacrylate skin layers made using PMMA alone. The optical bodywith the PMMA/PELESTAT 10 wt. % blend polyacrylate blend skin layer hadbetter warp resistance than the optical body with the PMMA/PELESTAT 5wt. % blend polyacrylate blend skin layer.

Example 2

A multi-layer reflective polarizer could be constructed with firstoptical layers comprising PEN (polyethylene naphthalate) and secondoptical layers comprising coPEN (copolyethylene naphthalate). The PENand coPEN would be coextruded through a multi-layer melt manifold andmultiplier to form 825 alternating first and second optical layers. Thismulti-layer film would also contain two internal and two externalprotective boundary layers of the same coPEN as the second opticallayers for a total of 829 layers. In addition, two structural externalskin layers would be coextruded on both sides of the optical layerstack. These polyacrylate blend skin layers would about 18 micrometersthick and comprised 85 wt. % PMMA (VO44 from Total Petrochemical) and 15wt. % anti-static polymer (PELESTAT 300 from Sanyo Chemical Industries)would be formed over the PMMA blend structural layers. An extruded caseweb of the above-construction would then be heated in a tentering ovenwith air at 150° C. for 45 seconds and then uniaxially oriented at a 6:1draw ratio.

Example 3

A multi-layer reflective polarizer could be constructed with firstoptical layers comprising PEN (polyethylene naphthalate) and secondoptical layers comprising coPEN (copolyethylene naphthalate). The PENand coPEN would be coextruded through a multi-layer melt manifold andmultiplier to form 825 alternating first and second optical layers. Thismulti-layer film would also contain two internal and two externalprotective boundary layers of the same coPEN as the second opticallayers for a total of 829 layers. In addition, two structural externalskin layers would be coextruded on both sides of the optical layerstack. These polyacrylate blend skin layers would be about 18micrometers thick and comprised 60 wt. % PMMA (VO44 from TotalPetrochemical) and 40 wt. % PVDF (SOLEF 1008 from Soltex PolymerCorporation. Strippable skin layers formed from a blend of 96 wt. %syndiotactic polypropylene (PP1571 from Total Petrochemical) and 4 wt. %anti-static polymer (PELESTAT 300 from Sanyo Chemical Industries) wouldbe formed over the PMMA blend structural layers. An extruded cast web ofthe above construction would then be heated in a tentering oven with airat 150° C. for 45 seconds and then uniaxially oriented at a 6:1 drawratio.

Example 4

A multi-layer reflective polarizer could be constructed with firstoptical layers comprising PEN (polyethylene naphthalate) and secondoptical layers comprising coPEN (copolyethylene naphthalate). The PENand coPEN would be coextruded through a multi-layer melt manifold andmultiplier to form 825 alternating first and second optical layers. Thismulti-layer film would also contain two internal and two externalprotective boundary layers for a total of 829 layers. In addition, twostructural external skin layers would be coextruded on both sides theoptical layer stack. These polyacrylate blend skin layers would be about18 micrometers thick and comprised 84 wt. % PMMA (VO44 from TotalPetrochemical), 15 wt. % antistatic polymer (PELESTAT 300 from SanyoChemical Industries), and 1 wt % UVA (TINUVIN 1577 from Ciba SpecialtyChemical). Strippable skin layers formed from a blend of 96 wt %syndiotactic polypropylene (PP 1571 from Total Petrochemical) and 4 wt %anti-static polymer (PELESTAT 300 from Sanyo Chemical Industries) wouldbe formed over the PMMA blend structural layers. An extruded cast web ofthe above construction would then be heated in a tentering oven with airat 150° C. for 45 seconds and then uniaxially oriented at a 6:1 drawratio.

Example 5

Biaxially oriented multi-layer optical films could be made with similarpolymer constructions to the above examples for use as a Visible Mirror.

Example 6

A multi-layer film was coextruded with PEN (0.48 IV PEN available from3M Company) core layers, PMMA (VO44 available from Total Petrochemical)inner skin layers, and syndiotactic polypropylene (PP1571 from TotalPetrochemical) outer skin layers using a 5 layer feedblock and extrusiondie. The PEN layers were extruded at 20 lbs/hr using a 1.5″ single screwextruder. The PMMA inner skin layers were extruded at 10 lbs/hr using a25 mm twin screw extruder. The syndiotactic polypropylene layers wereextruded at 5 lbs/hr using a 1.0″ single screw extruder. The multi-layerfilm was cast onto a chilled roll with a temperature of 90° F. at 9.5fpm to form a 20 mil cast web.

The 20 mil cast web was then biaxially oriented in a batch orientationprocess by first preheating the web for 50 seconds at 150° C. and thenstretching the cast web at 100%/second and draw ratios of 3.5×3.5.

After first removing the strippable syndiotactic polypropylene skinlayers, this film was then exposed to a light source of 1200 kJ/m² at340 nm in a test run according to ASTM G155 using a water-cooled xenonarc with daylight filters. The film exhibited an optical densityincrease of 0.0614 at 420 nm.

Example 7

A multi-layer film with PEN core layers, PMMA inner skin layers, andsyndiotactic polypropylene outer skin layers was produced as describedin Example 6 with the addition of lwt % Tinuvin 1577 and 0.5 wt %CHIMASSORB 119 (HALS available from Ciba Speciality Chemicals) to thePMMA inner skin layers.

Example 8

A multi-layer film with PEN core layers, PMMA inner skin layers, andsyndiotactic polypropylene outer skin layers was produced as describedin Example 6 with the addition of 2 wt % TINUVIN 1577 to the PMMA innerskin layers.

Example 9

A multi-layer film with PEN core layers, PMMA inner skin layers, andsyndiotactic polypropylene outer skin layers was produced as describedin Example 6 with the addition of 3 wt % TINUVIN 1577 and 1.0 wt %CHIMASSORB 119 to the PMMA inner skin layers.

After first removing the strippable syndiotactic polypropylene skinlayers, this film was then exposed to a light source of 1200 kJ/m² at340 nm in a test run according to ASTM G155 using a water-cooled xenonarc with daylight filters. The film exhibited an optical densityincrease of 0.0361 at 420 nm.

Example 10

A multi-layer film with PEN core layers, PMMA inner skin layers, andsyndiotactic polypropylene outer skin layers was produced as describedin Example 6 with the addition of lwt % TINUVIN 1577 and 0.5 wt %CHIMASSORB 944 (HALS available from Ciba Speciality Chemicals) to thePMMA inner skin layers.

Example 11

A multi-layer film with PEN core layers, PMMA inner skin layers, andsyndiotactic polypropylene outer skin layers was produced as describedin Example 6 with the addition of 3 wt % TINUVIN 1577 and 1.0 wt %CHIMASSORB 944 to the PMMA inner skin layers.

Example 12

A multi-layer film was coextruded with PET (0.74 IV PET available fromEastman Company) core layers, coPMMA (75 mol % methyl methacrylate and25 mol % ethyl acrylate known as CP63 available from TotalPetrochemical) inner skin layers, and syndiotactic polypropylene (PP1571from Total Petrochemical) outer skin layers using a 5 layer feedblockand extrusion die. The PET layers were extruded at 20 lbs/hr using a1.5″ single screw extruder. The coPMMA inner skin layers were extrudedat 10 lbs/hr using a 25 mm twin screw extruder. The syndiotacticpolypropylene layers were extruded at 5 lbs/hr using a 1.0″ single screwextruder. The multi-layer film was cast onto a chilled roll with atemperature of 90° F. at 9.5 fpm to form a 20 mil cast web.

The 20 mil cast web was then biaxially oriented in a batch orientationprocess by first preheating the web for 50 seconds at 100° C. and thenstretching the cast web at 100%/second and draw ratios of 4×4.

After first removing the strippable syndiotactic polypropylene skinlayers, this film was then exposed to a light source of 1200 kJ/m² at340 nm in a test run according to ASTM G155 using a water-cooled xenonarc with daylight filters. The film exhibited an optical densityincrease of 0.0189 at 420 nm.

Example 13

A multi-layer film with PET core layers, coPMMA inner skin layers, andsyndiotactic polypropylene outer skin layers was produced as describedin Example 12 with the addition of lwt % TINUVIN 1577 and 0.5 wt %CHIMASSORB 119 to the coPMMA inner skin layers.

Example 14

A multi-layer film with PET core layers, coPMMA inner skin layers, andsyndiotactic polypropylene outer skin layers was produced as describedin Example 12 with the addition of 2 wt % TINUVIN 1577 to the coPMMAinner skin layers.

Example 15

A multi-layer film with PET core layers, coPMMA inner skin layers, andsyndiotactic polypropylene outer skin layers was produced as describedin Example 12 with the addition of 3 wt % TINUVIN 1577 and 1.0 wt %CHIMASSORB 119 to the coPMMA inner skin layers.

After first removing the strippable syndiotactic polypropylene skinlayers, this film was then exposed to a light source of 1200 kJ/m² at340 nm in a test run according to ASTM G155 using a water-cooled xenonarc with daylight filters. The film exhibited an optical densityincrease of 0.0058 at 420 nm.

Example 16

A multi-layer film with PET core layers, coPMMA inner skin layers, andsyndiotactic polypropylene outer skin layers was produced as describedin Example 12 with the addition of 1 wt % TINUVIN 1577 and 0.5 wt %CHIMASSORB 944 to the coPMMA inner skin layers.

Example 17

A multi-layer film with PET core layers, coPMMA inner skin layers, andsyndiotactic polypropylene outer skin layers was produced as describedin Example 12 with the addition of 3 wt % TINUVIN 1577 and 1.0 wt %CHIMASSORB 944 to the coPMMA inner skin layers.

All references and publications cited herein are expressly incorporatedherein by reference in their entirety into this disclosure. Illustrativeembodiments of this disclosure are discussed and reference has been madeto possible variations within the scope of this disclosure. These andother variations and modifications in the disclosure will be apparent tothose skilled in the art without departing from the scope of thisdisclosure, and it should be understood that this disclosure is notlimited to the illustrative embodiments set forth herein. Accordingly,the disclosure is to be limited only by the claims provided below.

What is claimed is:
 1. An optical body, comprising: an optical filmcomprising polyester, the optical film comprising alternating first andsecond optical layers, the first and second optical layers comprisingpolyesters; a first extruded skin layer disposed on a first side of theoptical film, the first extruded skin layer comprising a mixture of apolyacrylate and a second polymer, wherein the second polymer is notmiscible in the polyacrylate and has a refractive index of from 1.45 to1.53; and a first extruded strippable skin layer disposed on the firstextruded skin layer; wherein the first extruded skin layer, when exposedby removal of the first extruded strippable skin layer, is adapted toavoid adhesion to a glass surface and assists the optical body to resistwarping.
 2. The optical body of claim 1, further comprising: a secondextruded skin layer comprising polyacrylate disposed on a second side ofthe optical film; and a second extruded strippable skin layer disposedon the second extruded skin layer.
 3. The optical body of claim 1,wherein the optical film comprises an oriented multilayer optical film.4. The optical body of claim 1, wherein the optical film comprisespolyethylene terephthalate or copolyethylene terephthalate.
 5. Theoptical body of claim 1, wherein the optical film comprises polyethylenenaphthalate or copolyethylene naphthalate.
 6. The optical body of claim5, wherein the polyacrylate comprises a copolymer ofpolymethylmethacrylate.
 7. The optical body of claim 5, wherein thepolyacrylate comprises polymethylmethacrylate.
 8. The optical body ofclaim 1, wherein the second polymer comprises an anti-static polymer. 9.The optical body of claim 6, wherein the first extruded skin layerfurther comprises polyvinylidene fluoride.
 10. The optical body of claim1, wherein the first extruded skin layer further comprises a UVabsorber.
 11. The optical body of claim 1, wherein the first extrudedskin layer further comprises a UV absorber and a hindered amine lightstabilizer.
 12. The optical body of claim 1, wherein the first extrudedstrippable skin layer comprises a polyolefin.
 13. The optical body ofclaim 1, wherein the first extruded strippable skin layer comprises ananti-static polymer.
 14. The optical body of claim 1, wherein the firstextruded strippable skin layer comprises a continuous phase and adisperse phase.